Enzymatic opacifying composition for paper, pulp or paperboard, processes using same and pulp, paper or paperboard produced therefrom

ABSTRACT

An organic agent for enhancing opacity in paper, paperboard or pulp comprises a hydrolase or an oxido-reductase; this enzymatic opacifying agent overcomes drawbacks associated with traditional organic and inorganic opacifying agents but also serves to provide increased strength and reduced porosity in paper and paperboard.

FIELD OF THE INVENTION

This invention relates to a composition for use in making paper, pulp orpaperboard; and a process of making paper, pulp or paperboard employingthe composition, especially to add opacity to the paper, pulp orpaperboard and a paper, pulp or paperboard produced using thecomposition.

BACKGROUND OF THE INVENTION

In paper and paperboard manufacture, sheet formation is generallyobtained on wire webs in a wet end from pulp slurry and is followed bythe gradual removal of moisture in a press section and drier section. Acalender section follows the drier section with the purpose of obtaininga desired finish, for example, smoothness, thickness or gloss.

Despite the real advantages of using mechanical action to impart certaincharacteristics to the sheet, these advantages are limited.Complementary solutions for improving even further certain paper orpaperboard characteristics can be applied internally in the wet end orexternally with size-presses or coaters when these are available. Thesesolutions are related to the use of fillers and functional additives.

Fillers are generally white pigments that can be divided into two majorcategories:

-   a) regular fillers having wide application and cost lower than that    of cellulosic fiber, e.g. kaolin clay, ground calcium carbonate and    precipitated calcium carbonate;-   b) specialized fillers having usually lower volume applications and    costs sometimes comparable with or even higher than cellulosic    fiber; Some examples are: anatase titanium dioxide, rutile titanium    dioxide, composite pigments, e.g. clay and titanium dioxide, PSS    (precipitated synthetic silica—silica oxides and precipitated    silicate—aluminum silicate), talc (industrial grade hydrated    magnesium silicate), aluminum trihydrate, calcium sulfate, natural    or precipitated barium sulfate, zinc oxide, zinc sulfur—surface    treatments only, Satin White (calcium sulfo-aluminate    complex)—surface treatments only, urea formaldehyde resin (organic    pigment), plastic pigments (empty or full spheres)—surface    treatments only.

The advantages brought by fillers in paper or paperboard manufacture aremostly related to cost reductions, except with some of the specializedfillers, especially titanium dioxide. The process disadvantages arehowever important and concern mostly wire, felt, doctor blade, refinersabrasion, machine deposits increase, increased linting dust, breaksrelated to sheet strength decrease and filler retention difficultiesrequiring retention program solutions.

On the other hand, the functional advantages, with respect to finalproduct characteristics, brought by fillers are also important: opticalproperties, i.e. brightness and opacity, improvement, improvedprintability, better sheet formation, increased smoothness and improveddimensional stability. The functional disadvantages are mostly relatedto increased two sidedness, reduced rigidity, increased linting anddecreased sheet strength.

Improving the paper or paperboard characteristics beyond the mechanicallimits of a paper or paperboard machine often requires the use offillers for their functional advantages and the use of functionaladditives for even better results.

Examples of functional additives which can improve the sheetcharacteristics are dyes and optical brighteners, coating polymers, wetand dry strength resins, sizing agents, fluorocarbons, traditionalorganic opacifying agents and other specialty additives, while processadditives that improve the production process include biocides,deposit-control agents, felt conditioners and cleaners, defoamers, andeffluent treatments.

Traditional organic opacifying agents are important functional additivesused to improve the sheet characteristics obtained with mechanical meansand with filler use. Resistance to water penetration, better printingcharacteristics, increased opacity brightness and whiteness, increasedbulk and caliper, better formation, have been investigated and oftenobtained. Some process improvements related to reduced abrasion and costreduction have also been noticed in some cases.

The following examples illustrate some of the traditional organicopacifiers:

U.S. Pat. Nos. 5,296,024 and 5,292,363 disclose a composition forenhancing opaqueness in papermaking comprising the reaction product of afatty acid and a diamine.

Different US patents related to U.S. Pat. No. 5,296,024 indicate thatthe resulting amide of the diamine, which forms the cationic softenerbase, is the fatty acid monoamide or the diamide or a mixture thereof.

U.S. Pat. No. 5,488,139 describes an opacifier which is a reactionproduct of an alkanol amine and a dimerized acid, wherein the diamine(aminoethylethanol amine) is preferred, in this Patent, the principalreactant with the amine is a dimerized acid.

Despite the clear advantages traditional opacifiers bring topapermaking, functional limitations on their use related especially topaper sheet strength and porosity have been noticed in mill conditions.

A particular category of chemical additives with both funtional andprocess applications are enzymes, which are proteins with catalyticproperties.

The use of enzymes is ecologically interesting, and such enzymes cangenerally be applied anywere in the paper, paperboard or even pulpproduction. The following examples illustrate some of the present millor laboratory applications for enzymes:

-   -   Xylanases—for prebleaching and bleaching pulps, especially        Kraft.    -   Pectinases and xylanases—for debarking.    -   Laccases, proteases—for mechanical pulp refining    -   Cellulases and xylanases—for chemical pulp refining    -   Cellulases—for recycled pulp refining    -   Cellulases—for KAPPA number reduction in Kraft cooking    -   Xylanases—for brightness reversion    -   Cellulases, amylases, xylanases, lipases—for deinking    -   Cellulases—for tissue softness    -   Laccases—for mechanical pulp strength    -   Manganese peroxidases—for chemical pulp strength    -   Cellulases—for chemical fibre Tinting reduction    -   Laccases—for increased chemical fibre bulk    -   Cellulases and xylanases—for increased chemical fibre        flexibility    -   Cellulases—for reduced porosity and increased fibrilation of        chemical fibres    -   Cellulases and amylases—for increased drainage    -   Esterases—for stickies reduction    -   Amylases, proteases, levan hydrolase—for paper machine cleaning    -   Acetyl esterase, pectinases—for mechanical pulp white water        treatments    -   Peroxidases, laccases, catalases—for effluent treatments    -   Pectinases for cationic demand reduction in peroxide bleached        mechanical pulp

In the prior art, WO95/27825 discloses a preparation process forincreasing the content of inorganic fillers while maintaining orincreasing the Scott internal bond strength, by addition of a cellulasetype enzyme. Increasing the content of inorganic fillers is known in theart to be needed for particular applications; inorganic fillers functionas opacifiers.

Increasing the level of inorganic fillers for the majority of specificpaper grades very often equates into one or more of the followingdisadvantages:

-   -   Increased paper machine blades abrasion    -   Increased paper machine press rolls wear    -   Increased paper machine inorganic deposits and breaks    -   Increased chemical costs in papermaking (e.g. when TiO₂ is used)    -   Increased printer equipment abrasion

All these reasons justify the use of traditional organic opacifiersrather than inorganic filleras as opacifiers.

In the prior art. it was known that increasing the levels of inorganicfillers favors opacity increase, but also results in decrease instrength.

SUMMARY OF THE INVENTION

Surprisingly, while investigating porosity increase enzymaticapplications, it has now been discovered that some enzymes also improveopacity without the drawbacks associated with traditional organicopacifiers. The handsheets made with enzyme treated fibres were oftenless porous, with increased tensile strength as compared with theuntreated controls; and were much less porous, and exhibited much highertensile strength as compared with the traditional organic opacifiertreated handsheets.

In this invention, the opacity obtained with enzymes as opacifyingagents was higher or similar to that obtained with traditional organicopacifiers while porosity and strength properties were clearly improved.

Although the prior art such as WO95/27825 shows that a cellulase canincrease an internal bond strength of paper, the particular features ofthe present invention are absent from prior art. The prior art containsno showing that enzymes increase sheet opacity without an increase inthe content of opacifying inorganic fillers.

The enzymes which function as organic opacifying agents may be addedduring the course of paper and paperboard manufacturing processes; andcan also be used in the pulp manufacture stage.

It is an object of the present invention to provide an agent that addsopacity to paper, paperboard or pulp to which it is added.

It is another object of the present invention to provide an agent foradding to a pulp slurry of cellulosic fibers to enhance opacity withoutadversely affecting other properties.

It is another object of the invention to provide a method of enhancingopacity in a paper composition such as paper, paperboard or papermakingpulp.

It is yet another object of the invention to provide a process ofproducing paper or paperboard of enhanced opacity.

It is still another object of the invention to provide a papermakingstock, which stock may be formed into a paper or paperboard of enhancedopacity.

It is yet another object of this invention to provide an opacified papercomposition, for example a paper, paperboard or papermaking pulp ofenhanced opacity.

It is a specific object of the present invention to provide a processwherein an organic opacifying agent is added to recycled, deinked orvirgin pulp of cellulosic fibers to form a paper, paperboard or pulphaving desirable physical characteristics.

Still another specific object of the present invention is to provide aprocess for adding a composition to pulp slurry of cellulosic fibers ina papermaking process that results in a paper, paperboard or pulp havingenhanced opacity.

Another specific object of the present invention is to provide a paper,paperboard, pulp or pulp slurry having the desirable characteristic ofenhanced opacity.

In accordance with the invention, there is provided in a method ofenhancing opacity in a paper composition, in which an organic opacifyingagent is incorporated in the paper composition, the improvement whereinthe organic opacifying agent comprises an enzyme selected from the groupconsisting of hydrolases and oxidoreductases.

In accordance with another aspect of the invention, there is provided anopacifying agent for use in enhancing opacity in a paper compositionselected from paper, paperboard and papermaking pulp, comprising anenzyme selected from the group consisting of hydrolases andoxidoreductases.

In accordance with still another aspect of the invention, there isprovided a papermaking stock comprising: pulp slurry of papermakingfibers and an organic opacifying agent in an aqueous vehicle; saidorganic opacifying agent comprising an enzyme selected from hydrolasesand oxidoreductases.

In accordance with yet another aspect of the invention, there isprovided an opacified paper composition comprising papermaking fibersand an organic opacifying agent, wherein said organic opacifying agentcomprises an enzyme selected from the group consisting of hydrolases andoxidoreductases.

In accordance with yet another aspect of the invention, there isprovided a process of producing paper or paperboard of enhanced opacitycomprising: i) providing a pulp slurry of papermaking fibers, ii) addingan organic opacifying agent to said slurry, and iii) forming paper orpaperboard from said slurry, wherein said organic opacifying agentcomprises an enzyme selected from hydrolases and oxidoreductases.

DETAILED DESCRIPTION OF THE INVENTION

The invention employs an organic opacifying agent which avoidsdisadvantages associated with traditional inorganic opacifying agentswhile providing superior physical properties as compared with priororganic opacifying agents.

The organic opacifying agents of the invention comprise a hydrolase oran oxidoreductase enzyme. A preferred hydrolase is a cellulose(E.C.3.2.1.4); a preferred oxidoreductase is laccase (E.C.1.10.3.2).

Hydrolases are enzymes that catalyse the hydrolysis of a chemical bond,whereby a molecule is cleaved into two parts by the addition of amolecule of water. The catalysed reaction would have the following form:A-B+H₂O→A-OH+B-H

The chemical bonds cleaved in this way by hydrolysis include C—O, C—Nand C—C bonds or in the case of organophosphorous hydrolases even P—O,P—F and P—S bonds.

As shown indirectly in the pulp and paper enzymatic applications examplelist hereinbefore, hydrolases are a class of enzymes that benefit fromthe presence of an extremely large group of substrates available forenzymatic action, for example cellulose, hemicelluloses and many others,in conjunction with the presence of water in large quantities in thepulp, paper and paperboard processes.

Cellulases, in particular hydrolyse cellulose, which is an unbranchedglucose polymer composed of 1,4 glucose units linked by β-1,4-glycosidicbonds, and is the main component of pulp, by cleaving theβ-1,4-glycosidic bonds. Hydrolases which are cellulolytic enzymes can beclassified into three major types:

-   1.0 ENDOGLUCANASES, hydrolyzing randomly the polymeric chain (EC    3.2.1.4)-   2.0 EXOGLUCANASES, hydrolyzing the ends of the chain:    -   2.1.1 Cellobiohydrolases, eliberating cellobiose—the glucose        dimer (EC 3.2.1.91)        -   Cellobiohydrolases I: hydrolyzing the reducing end        -   Cellobiohydrolases II: hydrolyzing the non-reducing end        -   2.1.2 Glucanhydrolases, eliberating directly glucose (EC            3.2.1.74)-   3.0 β-GLUCOSIDASES or cellobiases, acting on cellobiose or soluble    cellodextrins (EC 3.2.1.21).

As shown indirectly in the pulp and paper enzymatic applications examplelist, oxidoreductases are a second class of enzymes that benefit fromthe presence of an extremely large group of substrates available forenzymatic action, for example lignin, cellulose, hemicelluloses and manyothers, in the pulp, paper and paperboard processes.

Oxidoreductases are enzymes that catalyse the transfer of electrons fromone molecule (oxidant or hydrogen donor or electron donor) to anothermolecule (reductant or hydrogen acceptor or electron acceptor). Thecatalyzed reation would have the following form:A⁻+B→A+B⁻

Laccases in particular (EC 1.10.3.2), surprisingly catalyse theoxidation of a large number of different substrates, while enzymes ingeneral, for example cellulases, are usually substrate specific.Phenolic lignin units, lignin is an aromatic heteropolymer ofphenyl-propanoid units, many phenolic compounds (diphenols, polyphenols,different substituted phenols), diamines, aromatic amines, benzenethiolsand some inorganics (e.g. iodine) are oxidised directly with molecularoxygen as final electron acceptor through laccase action, the oxygenbeing reduced to water.

Besides the presence of molecular oxygen, laccases may require organicmediators which are sometimes already present in the pulp slurry.

Suitable mediators, by way of example, are2-2′azinobis(3-ethylbenzthiazoline-6-sulfonate); ABTS1-hydroxybenzotriazole; HBT N-acetyl-N-phenylhydroxylamine or NHAvioluric acid or VIO N-hydroxybenzotriazole or NHB methyl3,5-dimethoxy-4-hydroxybenzoate; methyl syringate potassiumoctacyanomolybtate; 1-phenyl-3-methyl-pyrazolone sodium;1-phenyl-3methyl-4-methylamino-pyrazolone-5-N(4)-methanesulfonate; PPNa1-(3′sufophenyl)-3-methylpyrazolone-5); and SPP N-hydroxyphthalimide aswell as numerous phenoxazines and phenotiazines.

The laccase active site contains four copper atoms. In a reportedmechanism, the separate type 1 copper atom extracts one electron fromthe substrate, while the other copper atoms (one type 2 and two type 3)grouped in a trinuclear cluster receive the electron through presumablya conserved Hys-Cys-His tripeptide. Once the complete reduction in thetrinuclear center takes place it is followed by the molecular oxygenreduction.

The organic opacifying agent of this invention is usually added tobleached wood pulp or recycled paper pulp.

The organic opacifying agent of this invention can be added alone or inconjunction with sizing agents, brighteners and other opacifying agentsor any other functional or process additives.

The organic opacifying agent of this invention can be added to any pulpslurry, deinked or recycled pulp.

The amount of the opacifying agent and the other components added to thepulp slurry depends on the type of pulp slurry to which the opacyingagent is added.

The opacifying agent of this invention provides an increase in opacityto the paper, paperboard or pulp and provides an improved strength andporosity.

The opacifying agent may be employed in conjunction with a surfactantand stabilizing agents

Even though the opacying agent can be applied as a powder, typically itis dispersed in water for addition to the pulp slurry and typically isadded in an amount of 0.00002% to 2%, preferably 0.0002% to 0.2%,catalytic protein by weight, based on the oven dry weight of the pulpfibers.

The dispersion in water typically contains 0.1 to 30%, and preferablyabout 1-10%, by weight of the catalytic protein.

The opacifying agent of the invention is more efficient and moreeffective even at lower concentration than traditional organicopacifying agents.

The opacifying agent of the invention provides improved opacity to thetreated paper, paperboard or pulp.

A particular advantage of the present invention is that for a givenamount of inorganic filler, if present, in the paper, paperboard orpulp, which filler may or may not have opacifying properties, theopacity is enhanced by the organic, enzymatic opacifying agent. Moreespecially, it is not necessary to use an inorganic opacifying agent andit is not necessary to increase the content of an inorganic fillerhaving opacifying properties in order to increase the opacity, and whichincrease in content would result in loss of strength. The organic,enzymatic opacifying agent of the invention not only enhances theopacity but also increases the strength and lowers the porosity.

An inorganic filler is not required in order to provide opacity whenemploying the organic opacity agent of the invention; and the inventioncontemplates paper compositions containing the opacifying agent of theinvention and being free of inorganic filler, although inorganic fillersmay be included in the paper composition for the traditional purpose ofreducing the pulp content, without their necessity to provide anopacifying function.

The invention is further illustrated by reference to the Examples.

EXAMPLES Example 1

Laboratory opacity, brightness, porosity and tensile strength testingwere performed with the following materials and methods:

Pulp Preparation:

Water deionized at pH 7.0

Furnish: 400 g a.d. pulp: 10% deinked market pulp (40 g), 25% SoftwoodKraft (100 g a.d.), 65% Hardwood Kraft (260 g a.d.).

Additives:

Traditional organic opacifier (amide of fatty acid and diamine), TrizymDEO (trademark for a cellulase of Tri-Tex), PCC (without dispersant),TiO₂ (anatase), anionic PAM retention aid

Apparatus for Pulp Preparation:

Beater with controlled bedplate (Pile Valley Iron Works)

British disintegrator

Canadian standard freeness tester

150 microns mesh

Hotplate (Termolyne Cimarec 2™)

pH meter (VWR scientific model 8000)

Thermometer (Fisherbrand)

Caframo stirrer RZR50™

1000 ml beaker

In all trials (control/amide of fatty acid and diamine/cellulase) thepulp treatments were made as described below:

-   1) In a first stage refining was performed for the entire 400 g a.d.    of pulp according to TAPPI T 200 om-85 to a freeness of 300 ml CSF.    Following the refining, pulp consistency was adjusted to 3% by    filtration through a 150 micron mesh.-   2) In the second stage 30 g a.d./trial of fibre (1000 g pulp) were    heated and maintained at 55° C. for 20 minutes with opacifier    additions or with no opacifier additions (control) in a 1000 ml    beaker on the hotplate, while stirring at 300 rpm. The opacifier    additions were made at 0.2% as is/a.d. fibre for Trizym DEO    (trademark for a cellulase of Tri-Tex) and at 0.2% dry/a.d. fibre    for the traditional organic opacifier (amide of fatty acid and    diamine)-   3) In the third stage 15% PCC (4.5 g dry) and 15% TiO₂ (4.5 g dry)    addition was followed by 10 minutes of stirring while maintaining    55° C. pulp temperature.-   4) In the fourth stage the heating was stopped and the pulp was    diluted to 1% with the addition of 2000 g deionized room temperature    water, followed by 0.1% (0.03 g dry) anionic PAM addition and 2    minutes stirring at 200 rpm.

Handsheet preparation for optical testing was made with a slightmodification of TAPPI T 218 om-83 without a dispersion stage, withconditioning (without preconditioning) according to TAPPI T 402 om-88for 5 hours at 23° C. and 51% RH. The modification aimed at improvedmonitoring of the effect of fines and white water recirculation onopacity, concerned reusing three times the white water resulting fromsheet formation and retaining for testing only each fourth sheet.

Handsheet preparation for physical testing was made with a slightmodification of TAPPI T 205 om-83, with conditioning (withoutpreconditioning) according to TAPPI T 402 om-88 for 5 hours at 23° C.and 51% RH. The second modification aimed at improved monitoring of theeffect of fines and white water recirculation on porosity, concernedreusing three times the white water resulting from sheet formation andretaining for testing only each fourth sheet.

Handsheet printing opacity (ISO standard 2471) and ISO brightnesstesting were made in the conditioning temperature and humidityconditions after 5 hours from the handsheet preparation on a TechnibriteMicro TB-1C™.

Handsheet tensile strength (TAPPI T 220 om-88 and TAPPI T 494 om-88) andthe air resistance of paper (TAPPI T 460 om-88) were tested in theconditioning temperature and humidity conditions after 5 hours from thehandsheet preparation with a MC TEC vertical tensile tester and aUEC-1012—A densometer tester. ISO ISO Densometer Tensile TrialBrightness Opacity sec/100 ml Strength nr. % % air kN/m 1 Control 86.5080.69 63 4.8 2 amide of 86.88 81.58 55 4.4 fatty acid and diamine 3cellulase 86.91 82.71 121 5.4

Example 2

Laboratory opacity, brightness, porosity and tensile strength testingwere performed with the following materials and methods:

Pulp Preparation:

Water deionized at pH 7.0

Furnish: 400 g a.d. pulp: 10% deinked market pulp (40 g), 10% AspenBCTMP (40 g) 25% Softwood Kraft (100 g a.d.), 55% Hardwood Kraft (220 ga.d.).

Additives:

Traditional organic opacifier (amide of fatty acid and diamine), TrizymDLC (trademark for a laccase of Tri-Tex), PCC (without dispersant), TiO₂(anatase), anionic PAM retention aid

Apparatus for Pulp Preparation:

Beater with controlled bedplate (Pile Valley Iron Works)

British disintegrator

Canadian standard freeness tester

150 microns mesh

Hotplate (Termolyne Cimarec 2™)

pH meter (VWR scientific model 8000)

Thermometer (Fisherbrand)

Caframo stirrer RZR50™

1000 ml beaker

In all trials (control/amide of fatty acid and diamine/laccase) the pulptreatments were made as described below:

-   5) In a first stage refining was performed for the entire 400 g a.d.    of pulp according to TAPPI T 200 om-85 to a freeness of 300 ml CSF.    Following the refining, pulp consistency was adjusted to 3% by    filtration through a 150 micron mesh.-   6) In the second stage 30 g a.d./trial of fibre (1000 g pulp) were    heated and maintained at 55° C. for 20 minutes with opacifier    additions or with no opacifier additions (control) in a 1000 ml    beaker on the hotplate, while stirring at 300 rpm. The opacifier    additions were made at 0.2% as is/a.d. fibre for Trizym DLC    (trademark for a laccase of Tri-Tex) and at 0.2% dry/a.d. fibre for    the traditional organic opacifier (amide of fatty acid and diamine)-   7). In the third stage 15% PCC (4.5 g dry) and 15% TiO₂ (4.5 g dry)    addition was followed by 10 minutes of stirring while maintaining    55° C. pulp temperature.-   8) In the fourth stage the heating was stopped and the pulp was    diluted to 1% with the addition of 2000 g deionized room temperature    water, followed by 0.1% (0.03 g dry) anionic PAM addition and 2    minutes stirring at 200 rpm.

Handsheet preparation for optical testing was made with a slightmodification of TAPPI T 218 om-83 without a dispersion stage, withconditioning (without preconditioning) according to TAPPI T 402 om-88for 5 hours at 23° C. and 51% RH. The modification aimed at improvedmonitoring of the effect of fines and white water recirculation onopacity, concerned reusing three times the white water resulting fromsheet formation and retaining for testing only each fourth sheet.

Handsheet preparation for physical testing was made with a slightmodification of TAPPI T 205 om-83, with conditioning (withoutpreconditioning) according to TAPPI T 402 om-88 for 5 hours at 23° C.and 51% RH. The second modification aimed at improved monitoring of theeffect of fines and white water recirculation on porosity, concernedreusing three times the white water resulting from sheet formation andretaining for testing only each fourth sheet.

Handsheet printing opacity (ISO standard 2471) and ISO brightnesstesting were made in the conditioning temperature and humidityconditions after 5 hours from the handsheet preparation on a TechnibriteMicro TB-1C™.

Handsheet tensile strength (TAPPI T 220 om-88 and TAPPI T 494 om-88) andthe air resistance of paper (TAPPI T 460 om-88) were tested in theconditioning temperature and humidity conditions after 5 hours from thehandsheet preparation with a MC TEC vertical tensile tester and aUEC-1012—A densometer tester. ISO ISO Densometer Tensile TrialBrightness Opacity sec/100 ml Strength nr. % % air kN/m 1 Control 86.1180.51 52 4.3 2 amide of 86.48 81.38 45 4.0 fatty acid and diamine 3laccase 86.53 81.59 57 5.1

1. In a method of enhancing opacity in a paper composition, in which an organic opacifying agent is incorporated in the paper composition, the improvement wherein the organic opacifying agent comprises an enzyme selected from the group consisting of hydrolases and oxidoreductases.
 2. A method according to claim 1, wherein the paper composition is a paper or paperboard and wherein the organic opacifying agent is incorporated in a papermaking pulp slurry and the pulp slurry is formed into the paper or paperboard.
 3. A method according to claim 1, wherein the paper composition is a papermaking pulp and wherein the organic opacifying agent is incorporated in a slurry of the papermaking pulp.
 4. A method according to claim 1, wherein said enzyme is a hydrolase.
 5. A method according to claim 4, wherein said hydrolase is a cellulase.
 6. A method according to claim 1, wherein said enzyme is an oxidoreductase.
 7. A method according to claim 6, wherein said oxidoreductase is a laccase.
 8. A method according to claim 7, wherein said organic opacifying agent further comprises a mediator.
 9. A method according to claim 1, wherein said enzyme is incorporated in said paper composition in an amount of 0.00002 to 2%, by weight, catalytic protein based on the oven dry weight of pulp fibers of said paper composition.
 10. A method according to claim 9, wherein said amount is 0.0002 to 0.2%, by weight, catalytic protein based on the oven dry weight of pulp fibers of said paper composition.
 11. An opacifying agent for use in enhancing opacity in a paper composition selected from paper, paperboard and papermaking pulp, comprising an enzyme selected from the group consisting of hydrolases and oxidoreductases.
 12. An agent according to claim 11, wherein said enzyme is associated with at least one surfactant or stabilizing agent.
 13. An agent according to claim 11, wherein said enzyme is a cellulase or a laccase.
 14. A papermaking stock comprising: pulp slurry of papermaking fibers and an organic opacifying agent in an aqueous vehicle; said organic opacifying agent comprising an enzyme selected from hydrolases and oxidoreductases.
 15. A papermaking stock according to claim 14, wherein said slurry further comprises at least one papermaking additive selected from the group consisting of fillers, brighteners and sizing agents.
 16. A papermaking stock according to claim 14, wherein said enzyme is selected from cellulases and laccases, and is present in said slurry in an amount of 0.00002 to 2%, by weight catalytic protein, based on the oven dry weight of papermaking fibers.
 17. An opacified paper composition comprising papermaking fibers and an organic opacifying agent, wherein said organic opacifying agent comprises an enzyme selected from the group consisting of hydrolases and oxidoreductases.
 18. An opacified paper composition according to claim 17, wherein said enzyme is a hydrolase or laccase, and said enzyme is present in an amount of 0.00002 to 2%, by weight catalytic protein, based on the oven dry weight of papermaking fibers.
 19. A process of producing paper or paperboard of enhanced opacity comprising: i) providing a pulp slurry of papermaking fibers, ii) adding an organic opacifying agent to said slurry, and iii) forming paper or paperboard from said slurry, wherein said organic opacifying agent comprises an enzyme selected from hydrolases and oxidoreductases.
 20. A process according to claim 19, wherein said enzyme is a cellulase or a laccase, and said enzyme is in an amount of 0.00002 to 2%, by weight, catalytic protein based on the oven dry weight of papermaking fibers. 